1. Field of the Invention
This invention relates to hydraulic valve lifters as used in the valve trains of internal combustion engines and, more particularly to hydraulic valve lifters of the self-contained type in which a fluid is sealed within the assembly without provision for its replacement from any external source during operation.
2. Discussion of the Background
In a conventional self-containing hydraulic valve lifter such as shown in FIG. 2, the self-containing valve lifter 50 comprises a lifter body 51 and a plunger 52 slidably mounted in the body 51. A seat member 53 fixed to an upper opening portion of the body 51 engages with a push rod seat (not shown). A lower end of the body 51 engages with a cam (not shown). A fluid pressure chamber 54 is formed between the body 51 and a bottom wall of the plunger 52 and reservoir chamber 55 is formed within the plunger 55.
A check valve in the form of ball 57 is disposed in the pressure chamber 54 to close an aperture 56 formed in the bottom wall of plunger 52. The check valve 57 permits one-way fluid flow only from the reservoir chamber 55 to the pressure chamber 54.
A free piston 58 is slidably mounted in the plunger 52. The piston 58 is biased downwardly by a spring 59 and acts to absorb the changing quantity of fluid in the reservoir chamber 55. The plunger 52 is biased upwardly by a spring 60 disposed in the pressure chamber 54.
In this conventional valve lifter 50, due to the structure allowing the free piston 58 to be slidably mounted in the plunger 52, the diameter of pressure chamber 54 is set to be larger than that of the free piston 58. Therefore, when the valve lifter 50 is pressed downwardly in passing through a complete stroke thereof from the free condition in response to the rotation of the cam, the vertical stroke of the free piston 58 is larger than that of the complete stroke of the valve lifter 50. As a result, the total inner length 1 of the plunger 52 accommodating the free piston 52 is required to be longer. Therefore, the total length of the valve lifter 50 is increased and installation of the valve lifter 50 is more difficult.